Method of making a tower packing element

ABSTRACT

A cellular ceramic tower packing element. The tower packing element has an irregular, textured outer surface that provides a relatively large accessible surface area for the phase interaction of fluids. The tower packing elements are preferably spherical in shape and formed from cellular glass nodules that have a cellular core of a plurality of individual completely closed cells and a thin, continuous outer skin. The surface of the nodule is abraded or milled to remove the thin, continuous outer skin and a portion of the layer of underlying closed cells to rupture or open the individual cells in the layer beneath the outer skin. The inner surface of the opened and exposed cells form the exterior surface of the tower packing element and provide an irregular textured exterior surface with each exposed cell cavity forming a recessed portion or a micro-cup in the tower packing element exterior surface. The tower packing element, because of its cellular structure is relatively light in weight. The tower packing elements may be randomly packed in a tower to form a multiplicity of different types of passageways for the flow of fluids therethrough. The method of this invention contemplates treating cellular ceramic material by milling or abrading to expose the adjacent inner surfaces of the cell cavities to thereby enlarge or increase the accessible surface area of the tower packing element.

llnited States Patent Lastellucci [54] METHOD OF MAKING A TOWER PACKING ELEMENT [72] Inventor: Nicholas T. Castellucci, Pittsburgh, Pa.

[7f] Assignee: Pittsburgh Corning Corporation, Pittsburgh. Pa.

[22 Filed: Sept. 8, 1969 [21] Appl. No.: 856,104

Related US. Application Data [62] Division of Ser. No. 727.242. May 7. 1968. Pat. No.

Primary Iitaminer-Lester M. Swingle Attorney-Stanley J. Price, Jr.

[57] ABSTRACT A cellular ceramic tower packing element. The tower packing element has an irregular, textured outer surface that provides a relatively large accessible surface area for the phase inte raction of fluids. The tower packing elements are preferably spherical in shape and formed from cellular glass nodules that have a cellular core of a plurality of individual completely closed cells and a thin, continuous outer skin. The surface of the nodule is abraded or milled to remove the thin, continuous outer skin and a portion of the layer of underlying closed cells to rupture or open the individual cells in the layer beneath the outer skin. The inner surface of the opened and exposed cells form the exterior surface of the tower packing element and provide an irregular textured exterior surface with each exposed cell cavity forming a recessed portion or a micro-cup in the tower packing element exterior surface. The tower packing element, because of its cellular structure is relatively light in weight. The tower packing elements may be randomly packed in a tower to form a multiplicity of different types of passageways for the flow of fluids therethrough. The method of this invention contemplates treating cellular ceramic material by milling or abrading to expose the adjacent inner surfaces of the cell cavities to thereby enlarge or increase the accessible surface area of the tower packing element.

4 Claims, 4 Drawing Figures PATENTEDAPR 2 5 I972 FIGURE 4 FIGURE 3 INVENTOR.

IV/CHOLAS 7. CASTELL UCC/ H/S ATTORNEY METHOD OF MAKING A TOWER PACKING ELEMENT CROSS REFERENCE TO RELATED APPLICATIONS This application is a division of my application Ser. No. 727,242, filed May 7, 1968, now U.S. Pat. No. 3,493,218, dated Feb. 3, 1970.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a cellular tower packing element having a relatively large accessible area for the phase interaction of fluids and the method of making the tower packing element. More particularly, the invention relates to cellular tower packing elements having a generally spherical configuration with an irregular, textured surface formed by the inner surface of opened or exposed cell cavities and the method of making the tower packing element from a cellular ceramic nodule.

2. Description of the Prior Art In gas-liquid contacting operations, such as distillation, absorption and desorption, one of the most commonly used contacting devices is the so-called packed tower, wherein the liquid flows downwardly over a packing material, usually in countercurrent relation to a gas that flows upwardly through the packing. The purpose of the packing material is to provide a relatively large surface area over which the liquid may flow as a relatively thin film while at the same time, providing passages for gas flow and permitting the gas to flow over and in intimate contact with the liquid film on the surfaces of the packing elements.

To maintain a high operating efficiency in the gas-liquid contacting operation, a number of factors must be considered. The packing material must be such that the pressure drop across the column is maintained at a relatively low level. The packing material should be chemically inert in the presence of the fluids that pass through the column. The packing material should be sufficiently light to produce an acceptable transverse loading on the tower walls. The packing material should also have a high mechanical durability and be relatively nonabsorbent and impervious to the fluids that flow through the tower.

Tower packing elements have been made from numerous materials. Among the materials which have been employed are porcelain, carbon steel, stainless steel and other metals, glass and plastics such as polyethylene and polypropylene. The ceramic materials, metals and glass are the preferred materials from which tower packing elements are fabricated. The plastic materials have, in general, been suitable only for low temperature uses and with relatively inert solvents and solutes.

Numerous shapes of tower packing elements have been employed in the past. Among the more commonly employed shapes are Raschig rings, Berl saddles and glass helixes. Cylinders and spheres have also been used. A wire helix form of packing element is disclosed in U.S. Pat. No. 2,135,703. A generally helical shaped packing element is shown in U.S. Pat. No. 3,167,600. A generally star-shaped packing element is shown in U.S. Pat. No. 2,198,861.

Iri U.S. Pat. No. 3,170,969, a coated tower packing element is disclosed. In this patent, the problem of mass transfer efficiency is discussed and how the mass transfer efficiency can be increased by applying a thin coating of sub-microscopic silica particles to the external surfaces of the tower packing element. It is stated that the coating increases the liquid filming over the external surfaces of the packing element and hence, increases its mass transfer efficiency.

SUMMARY OF THE INVENTION In accordance with the present invention, a tower packing element has been found that has an improved separating power when compared with conventional tower packing elements of various configurations. The tower packing element is generally spherical in shape and has an irregular textured external surface. It is believed that this irregular, textured external surface increases the accessible surface area for the phase interaction of the fluids during the gas-liquid contacting operation. The irregular, textured surface may be obtained by milling or abrading a cellular ceramic nodule until the continuous outer skin and a portion of the layer of underlying closed cells are removed. The milling or abrading of the cellular ceramic nodule ruptures or opens the individual cells in the layer beneath the outer skin. The surface of the tower packing element then comprises the inner surface of the opened and exposed cells to provide an irregular textured exterior surface with each exposed cell cavity forming a recessed portion or a micro-cup in the tower packing element exterior surface.

Accordingly, the principal object of this invention is to provide a tower packing element that has a relatively large accessible surface area formed by the inner surface of a layer of opened or ruptured cells on the surface of the tower packing element.

Another object of this invention is to provide a method of forming a tower packing element with an irregular textured exterior surface from a cellular nodule having a relatively smooth continuous outer skin.

These and other objects and advantages of this invention will be more completely disclosed and described in the following specification, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF TI-IE DRAWINGS FIG. 1 is a perspective view, partly in section, illustrating a cellular glass nodule from which the tower packing element is formed.

FIG. 2 is a fragmentary section of the cellular nodule illustrated in FIG. 1 after the surface of the nodule has been abraded or milled to open or expose the underlying layer of cells beneath the skin of the nodule.

FIG. 3 is a view in elevation and in section illustrating a distillation tower with the tower packing elements of this in vention positioned therein.

FIG. 4 is a schematic representation illustrating the placing of the spherical nodules in a drum and rotating the drum to abrade the nodules.

DESCRIPTION OF THE PREFERRED EMBODIMENT The cellular ceramic tower packing element of this invention provides a substantially improved packing material for a liquid-vapor contact environment. The tower packing element may be formed from a cellular glass nodule that is disclosed in U.S. Pat. No. 3,354,024. Since the method of manufacture and the structure of the cellular glass nodule is completely described in this patent, the cellular nodule and its process of manufacture will be described herein only to the extent necessary for an understanding of the present invention. The description of the cellular nodule as set forth in U.S. Pat. No. 3,354,024 is, however, incorporated herein by reference. The cellular glass nodules are made by first admixing relatively fine glass particles with a cellulating agent such as carbon black or the like. A binder and a fiuxing agent are added to this admixture. The admixture is then pelletized and the pellets are coated with a glass former that also serves as a parting agent during the cellulation process. The coated pellets are dried in a manner that a major portion of the fluxing agent migrates to the outer surface of the pellet.

The coated pellets are heated in a rotary furnace or kiln to a cellulating temperature at which the pellets bloat or cellulate. A portion of the fiuxing agent that has migrated to the surface of the pellet reacts with the glass former to form a thin, continuous outer skin of vitrified or glass-like material. The glass former also serves, during the cellulation process, as a parting agent to prevent nodules from adhering to each other.

The cellular glass nodule thus produced has a core of individual, completely closed cells of glassy material and a continuous outer skin of a glassy material that has a composition different than the composition of the cellular core. The cellular glass nodules have a density of between about 6 pounds per cubic foot and 25 pounds per cubic foot. The nodules may be made, within limits, in various diameters by controlling the size of the pellet or the degree of cellulation. It is well known that the desirable size of a tower packing element is dependent on the diameter of the tower or column and, with the process described in US. Pat. No. 3,354,024, and the herein described process, the size or diameter of the tower packing element can be controlled within narrow limits.

The cellular glass nodule made according to the process described in the above-mentioned patent has a continuous outer skin of glassy material and is generally spherical in shape. Beneath this continuous outer skin of glassy material there is a layer of individual, completely closed cells. The cellular glass nodules with the outer continuous skin is impervious and does not absorb liquids. Since the plurality of individual cells beneath the outer skin are all closed cells, the inner core of the nodule remains impervious to fluids when the layer of cells beneath the surface of the nodule are ruptured or opened so that the core of the nodule, with the outer skin removed, remains impervious to fluids.

It was discovered by subjecting the cellular glass nodules to a treatment that removes the outer skin and opens or ruptures a layer of individual closed cells beneath the outer skin, the surface morphology of the nodule as a tower packing element is changed and there is a substantial increase in the surface area of the milled or abraded nodule for the phase interaction of fluids. The outer skin of the nodule and a portion of the cell walls therebeneath, may be removed by milling the surface of the nodule by placing the nodules in a ball mill and causing the nodules to be abraded, either through contact with adjacent nodules, or contact with other material placed in the ball mill for that purpose. The new surface of the nodule, after it has been subjected to the milling or abrading process, may be described as having substantially hemispherical recesses or micro-cups in the external surface. The cavities in the individual opened cells form the irregular, textured outer surface of the tower packing element.

Referring to the drawings, the cellular glass nodule in FIG. 1 is generally designated by the numeral 10. The cellular glass nodule 10 has a continuous outer skin 12 and a plurality ofindividual completely closed cells 14 that form the core of the nodule. As previously stated, the nodule made by the process described in U.S. Pat. No. 3,354,024, has the continuous outer skin 12. The surface area of the cellular glass nodule available for phase interaction of fluids is limited to the surface area defined by the continuous outer skin 12. When the nodule is subjected to a milling process, the outer skin 12 is removed and the layer of individual, completely closed cells beneath the skin 12 are also partially removed to form the new external surface ofthe tower packing element.

FIG. 2 illustrates a fragmentary portion of the nodule 10 after it has been subjected to milling to remove the outer skin 12 and a portion of the layer ofcells beneath the outer skin 12. In FIG. 2, the removed outer skin 12 is indicated by dash-dot phantom lines and the layer of cells beneath the removed skin 12 is generally designated by the numeral 16. Portions of the cell walls 18 of the individual cells 16 have been removed by the milling process so that recessed or micro-cup type recessed portions 20 are formed by the remaining cell walls 18 in the layer of cells 16 beneath the removed outer skin 12. It should be understood, although reference is made to the layer of cells 16 immediately beneath the outer skin 12, that the same surface configuration of the tower packing element 22 can be obtained by removing several layers of cells with the outer skin 12.

An example of the preferred method of converting the cellular glass nodule 10 to the tower packing element 22 is as follows.

Nodules of the type disclosed in US. Pat. No. 3,354,024, having a density of about l6 pounds er cubic foot and a diameter of about 4.5 mms. to about 7.5 mms. were placed in a rotatable drum. The drum was made of glass and had a diameter of about 6 inches and a length of about 9 inches. The drum was filled to about half capacity with the cellular glass nodules and was rotated at about rpm for about 6 hours. The outer skin 12 was removed by the abrasion between the nodules and the resultant tower packing elements 22 had a surface configuration similar to that illustrated in FIG. 2. It should be understood that other means for abrading the nodules 10 to form the tower packing elements 18 may be employed other than the above described method.

FIG. 3 illustrates a distillation column 24 that was used to compare the separating power of various commercially available tower packing elements and the tower packing element 22. The distillation column 24 includes a rectifying section 26 encased in a heating device 28 that maintained near adiabatic conditions in the column 26. The column was connected to a flask 30 that was encased in a heating mantle 32. The flask had a conventional packing support 34 that was positioned in the tapered opening 36 of the flask 30 and extended upwardly into the base of the rectifying section 26. The column 24 has a condenser 38 with a cooling means 40 connected to the upper end portion of the rectifying section 26. A condensate return 42 was provided in condenser 38 for return of the liquid. The tower packing elements 22 were positioned within the rectifying section 26 and supported on the support 34.

The previously described distillation column 24 is of conventional construction and does not form a part of this invention. It should be understood that the tower packing elements 22 may be employed in other types of liquid-gas contacting apparatus and it is not intended to limit the use of the tower packing elements 22 to the particular distillation column described.

In order to compare the different tower packing elements, the rectifying section 26 was packed in a random fashion to a depth of 183 cms. The rectifying column 26 had an inner diameter of 75 mms. The column was then heated for several hours and purged with an inert gas. The flask was charged with a 50-50 mol per cent mixture of trichloroethylene-n-heptane test solution. The rectifying section 26 was preheated by the heater 28 and the test mixture was heated in the flask 30 by the heating mantle 32. The column was permitted to operate under total reflux conditions for a period of six hours and thereafter, samples were removed from both the flask 30 and from the condenser 38 at the condensate return 42. Samples were taken at several liquid throughputs in this fashion and their composition determined. The total number of theoretical plates was then calculated in a known manner using Fenskes total reflux equation. The pressure drop of the packed column was also measured at different liquid throughputs and the liquid throughput at which flooding occurred was noted.

The separating power of a tower packing element may be conveniently expressed as the equivalent number of theoretical plates at a given liquid throughput. The higher the number of theoretical plates, the higher the separating power of the tower packing element. The pressure drop expressed at different throughputs and the throughput at which flooding occurs are other properties that determine the overall efficiency of a tower packing element. Thus, with the column 24, the separating power, i.e., the number of theoretical plates, the pressure drop at different liquid throughputs and the flooding throughput were measured.

Referring to FIG. 4, schematically illustrated is the abrasion process in which the outer skin of the smooth cellular glass nodule is removed, causing the nodule to be abraded. The smooth cellular glass nodules 10 are transferred from a bin 36 to a feeder device 38 that introduces the nodules to the rotatable drum 40. The nodules enter the rotatable drum through an axial tubular inlet 42. As the drum 40 rotates at a desired speed, the grinding action between adjacent nodules causes the outer skin of the smooth cellular glass nodules and a portion of the cell walls therebeneath to be removed. The same abrasion process may be accomplished by contact with the smooth cellular glass nodules and other material placed in the rotatable drum 40 for that purpose. After the nodules have been subjected to the abrading process, hemispherical recesses are formed in the external surface thereof. The hemispherical recesses form the irregular textured outer surface of 5 22 with a surface similar to that illustrated in FIG. 2.

The cellular ceramic tower packing elements having densities of 12.5 pounds per cubic foot, of 16.5 pounds per cubic foot, and of 23.0 pounds per cubic foot when compared with spherical glass beads were found to have superior separating power. For example, the cellular ceramic tower packing elements that have a density of 23 pounds per cubic foot at throughputs of about 10 liters per hour,

Another advantageous feature of the cellular ceramic tower packing element is that in comparison with similarly shaped glass beads the spherical glass beads were found to have a much lower pressure drop. This was confirmed by recording the pressure drop in the distillation column 24 at various throughputs for the cellular ceramic tower packing elements 22 having densities of 12.5 pounds per cubic foot, 16.5 pounds per cubic foot, and 23.0 pounds per cubic foot with the pres-' sure drop for the glass beads having a density of 16.0 pounds per cubic foot. Also, the column packed with the glass beads flooded at approximately 12.2 liters per hour throughput as compared with a throughput of liters per hour for the cellular ceramic tower packing elements 22 that had a density of about 16.5 pounds per cubic foot.

Similar tests were made with an n-heptane-methylcyclohexane test mixture. Cellular ceramic tower packing elements having densities of about 16.5 pounds per cubic foot and 23 pounds per cubic foot were compared with abraded glass beads and Raschig rings. A similar procedure was followed in this comparison. Conventional glass beads were milled in a ball mill in the presence of a silicon carbide abrasive for a period of two and one half hours to etch the surface and the cellular ceramic tower packing elements of this invention. The properties determined experimentally were throughput, pressure drop, void space, flood stage and separating power. These values are set forth in Table 1 below.

The data in Table 1 illustrates the per cent of void space for Berl Saddles and Raschig rings in a randomly packed column is much higher than cellular ceramic tower packing elements. For example, Raschig rings have a void space of 64.0 percent. This large free volume is represented as being the primary reason for large throughputs, high flood stage and low pressure drops obtained with this type of tower packing element. The cellular ceramic tower packing elements have 20 percent less void space. However, the pressure drop for the cellular ceramic nodules is lower, the throughputs are higher and the flood stage is higher. Of greater substance, however, is the fact that the cellular ceramic tower packing elements have a substantially greater separating power. For example, at a throughput of about 10 liters/hr, the separating power of the cellular ceramic tower packing elements 22 of 16 lbs/ft3 density is the equivalent of 26.5 theoretical plates. On the other hand, the Berl saddles at a throughput of 10 liters/hr. has a separating power that is equivalent to 20 theoretical plates. The difference in the separating power of the cellular ceramic tower packing elements having difierent densities is attributed to the surface morphology of the tower packing element.

In addition comparative tests, the separating power of the cellular tower packing elements having a size of approximately inch diameter and a density of about 16.0 pounds per cubic foot were compared with the separating power for A inch ceramic Berl saddles and the separating power of A inch glass Raschig rings at various throughputs. The comparative tests were made in separating a mixture of n-heptane and methyl cyclohexane. The cellular tower packing elements demonstrated a superior separating power.

In further comparative tests the pressure drop in the distillation column for the cellular tower packing elements having a size of approximately A inch diameter and a density of about 16.0 pounds per cubic foot again demonstrated improved pressure drop and throughput characteristics when compared with the 54: inch cellular ceramic Berl saddles, the A inch glass Raschig rings, A inch abraded glass beads, and A inch perforated glass beads.

Other advantageous features of the cellular ceramic tower packing elements are the light weight of the elements, the impervious nature of the closed cell structure and the ability to subject the tower packing elements to elevated temperatures. The tower packing elements 22 for the pressure discussed, preferably have a density of between 10 pounds per cubic foot and about 25 pounds per cubic foot. When compared with spherical glass beads having a density of 160 pounds per cubic TABLE 1 Test mixtu.ren-heptane/methy1 cyelohexane Void space random Pressure Through- The0- Flood packed, Drop P put retical stage Type packing percent (in. of Hg) (ml/hr.) plates (mL/hr.)

Perforated glass beads 6 mm. O.D 45. 0 20 5,000 18.0 15, 500

Abraded glass heads 6 mm. O.D 38. 0 10 5, 000 18. 0 14, 500

Berl saddles 6 mm. O.D 65.0 25 10, 000 20. 0 25,500

Raschig rings 6 mm. O.D 64. 0 10 5,000 13. 5 20,000

Cellular ceramic tower packing elements 16#/l'l;. 6 mm. O.D 46. 5 10 5, 000 27. 0 26,000

Cellular ceramic tower peeking elements 23#/ll:. 6 mm. O.D 46. 5 1O 5, 22. 0 22, 000

foot, it is apparent that the transverse wall loading of the packed column is substantially less with the cellular ceramic tower packing elements than with glass beads. Thus, the transverse wall effect or loading force placed upon the column wall will be substantially smaller with cellular ceramic tower packing elements. As a result, the column may be made of thinner material and may be more economically constructed. The low density of the cellular ceramic tower packing elements also requires less energy to heat the tower packing elements to reach total reflux conditions in the column. It was found with the binary mixtures herein disclosed total reflux conditions were attained in one third to one fourth the time with the cellular ceramic tower packing elements than with the other tower packing elements tested.

The cellular ceramic tower packing elements have a core of individual closed cells. The closed cells are impervious to liquids and vapors and the amount of liquid hold-up within the column is thus kept at a desired level. The tower packing elements being formed from cellular ceramic material may be subjected to relatively high distillation temperatures without either mechanical or chemical degradation.

While for purposes of illustration, specific reference has been made to a distillation column, it will be appreciated that the cellular ceramic tower packing elements may be advantageously employed in numerous other environments where a packing material is positioned in a liquid and vapor phase contacting region. The cellular ceramic tower pac k irig elements would be suitable, for example, for use in scrubbers, absorption towers and desorption towers. It should also be un-" derstood that the cellular ceramic tower packing elements may be made from materials other than formulated glass. It is believed one of the essential features of the power packing element is the textured, irregular external surface formed by the recessed portions of opened cells.

According to the provisions of the patent statutes, I have explained the principle, preferred construction and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment.

lclaim:

l. A method of making a tower packing element having an irregular textured external surface comprising,

obtaining a cellular ceramic material having a body portion of individual closed cells formed of cell walls and a continuous relatively smooth external skin forming a relatively smooth first surface, and

removing said continuous relatively smooth external skin and a portion of said cell walls of certain of the individual closed cells beneath the continuous external skin thereby forming a second relatively rough surface on said body portion comprising the remaining portions of said cell walls of the cells opened by removing said relatively smooth external skin and a portion of said cell walls, said second relatively rough surface having a greater surface area than said first relatively smooth surface.

2. A method of making a tower packing element as set forth in claim 1 which includes abrading the body portion to remove both the continuous external skin and a portion of the in- 20 dividual closed cells beneath the skin.

3. A method of making a tower packing element as set forth in claim 1 which includes,

forming said cellular ceramic material as a nodule having a substantially spherical shape with a continuous relatively smooth external skin, and

abrading the surface of said spherical nodule to remove said relatively smooth continuous skin and a portion of the individual closed cells beneath the outer skin and form a tower packing element having a substantially spherical shape.

4. A method of making a tower packing element as set forth in claim 3 which includes,

placing an inventory of said spherical nodules in a drum,

and

rotating said drum to abrade the nodules and remove said relatively smooth continuous skin and a portion of the individual closed cells beneath the outer skin.

I 32%??? UNIT-En STATES PATENT OFTTCE CERTIFICATE OF CORRECTION Patent: No. 3,657, 847 Dated April 1972 Inventor) Nicholas T. Castellucci It: is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, Line 75 "16 pounds er cubic foot" should read 16 pounds per cubic foot-- Column 5, Line 17 After about 10 liters per hour," insert:

have a separating 'power'of approfigimately l6 theoretical plates. The cellular ceramic tower elements with a density of 12.5 lbs. per cubic foot have a separating power of approximately 17 theoretical plates at the same throughput. The cellular ceramic tower packing elements with a density of 16.5 lbs. per. cubic foot have a separating power of approximately l9 theoretical plates through the range of throughputs between 5 and 18 liters per hour. It should be noted that the tower packing elements 22 are substantially spherical in shape and have the same shape as the spherical glass beads. This indicates that the superior separating power of the cellular ceramic tower packing elements is attributable at least in part, tothe irregular textured outer sur,::'ac-e. (End of paragraph) Column 6, Line 23 "In'addi tion comparative tests," should read In additional comparative tests, L.Column 7 Line 32 "of the power packing" should read v of the tower packing'- J Signed and sealed this 9th day of January l973 (SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. A method of making a tower packing element having an irregular textured external surface comprising, obtaining a cellular ceramic material having a body portion of individual closed cells formed of cell walls and a continuous relatively smooth external skin forming a relatively smooth first surface, and removing said continuous relatively smooth external skin and a portion of said cell walls of certain of the individual closed cells beneath the continuous external skin thereby forming a second relatively rough surface on said body portion comprising the remaining portions of said cell walls of the cells opened by removing said relatively smooth external skin and a portion of said cell walls, said second relatively rough surface having a greater surface area than said first relatively smooth surface.
 2. A method of making a tower packing element as set forth in claim 1 which includes abrading the body portion to remove both the continuous external skin and a portion of the individual closed cells beneath the skin.
 3. A method of making a tower packing element as set forth in claim 1 which includes, forming said cellular ceramic material as a nodule having a substantially spherical shape with a continuous relatively smooth external skin, and abrading the surface of said spherical nodule to remove said relatively smooth continuous skin and a portion of the individual closed cells beneath the outer skin and form a tower packing element having a substantially spherical shape.
 4. A method of making a tower packing element as set forth in claim 3 which includes, placing an inventory of said spherical nodules in a drum, and rotating said drum to abrade the nodules and remove said relatively smooth continuous skin and a portion of the individual closed cells beneath the outer skin. 